It is proposed to utilize the pH stat technique to study the process by which isolated segments of small intestine from the urodele, Amphiuma, alkalinize the mucosal media - a process which will be referred to as bicarbonate secretion. Sheets of small intestine will be mounted between halves of a lucite chamber that exposes 10.7 cm of stripped mucosa to 10 ml of oxygenated unbuffered media on its mucosal surface and a larger volume of the same media on its serosal surface. In other experiments a serosal solution containing 25 mM HCO3 ions gassed with a 95% 02, 5% CO2 mixture (pH 7.4) will be employed on the serosal side. The mucosal pH will be statted to 7.4 with an automatic titrator while the transmural potential is clamped at zero. The unidirectional fluxes of Na ion and Cl ion will be measured in paired adjacent segments in which HCO3 ion secretion is measured simultaneously. This study will aid in defining the role of HCO3 ion secretion in the transport of other electrolytes. In addition the effect of theophylline and cyclic AMP on these ion movements will allow a description of the base secretory process during the development of pathological states due to cholera or the enteric organisms.